(HAC) identifies those areas in the premises where flammable atmospheres can be found. It also provides an estimate as to how often these flammable atmospheres may be found. Flammable atmospheres are generally mixtures of air with flammable gas, Vapour, Dust or aerosol (Mist). For example, the head space in a tank containing a flammable solvent and the space surrounding the tank may both be classified as hazardous areas, but their classification would be different on grounds that flammable atmosphere could be continually present in one but rarely in the other.

Significance of HAC :

Originally HAC was used simply to enable process companies to make a correct choice of electrical equipment to prevent electrical ignition of the flammable solvent atmosphere by the equipment. Now, HAC is applied to help in wider risk assessment work and to help prevent other ignition sources such as electrostatic sparks. It is not only applied to areas where solvent vapour, gases or mist may be found but also their flammable dust clouds can occur. HAC, now has become a distinct area of concern and useful in whole range of industries.